Our computer-aided logic design system employs a synthesizer, a typical knowledgebased system. The register-transfer-leveldesign is described in digital system design language (DDL). The DDL translator generates a technology-independent functionaldesign from the DDL description, and the syntehsizer transforms the functional design into a technology-dependent gate-leveldesign. We implemented the synthesizer as a knowledge-based system because it works without an established algorithm and iseasy to modify according to the target technology. Our knowledge-based synthesizer for TTLICs generated a logic diagram ofalmost as high quality as one designed by a human expert. Only two CPU seconds are required for the FACOM M-380 to generatelogic diagrams containing 1000 gates, whereas a human designer takes one week. The CMOS gate array version was developed inonly one-half man-year, compared to four man-years for the original version